In automated systems and procedures, optical devices can be used to monitor particular elements of said systems and procedures. The optical device is used to capture an image of said elements of the system or procedure. Using image recognition techniques, the image can be analysed and the result of this analysis can be used, for instance, to monitor and influence the control of the system or procedure. A typical use of such an optical device in an automated system is the use of the optical system to read an optical code or barcode attached to a product to identify the type of product as well as for instance the batch number of the product used in the system or procedure.
From a financial aspect, it is advantageous and often required to use an optical device with a camera that can be produced for relatively low costs, such as a fixed focus camera. The quality of the images obtained with the fixed focus camera is often adapted to the specific task for which the optical device is employed.
However, when a fixed focus camera is used the distance between the fixed focus camera and the object of interest has to be carefully adjusted in order to allow the camera to produce images of the object of interest with a sufficient quality to allow the subsequent step of image recognition. In practice, it is desired to provide a user of an optical device with at least some margin with respect to the distance between the camera of the optical device and the object of interest, while keeping at the same time the quality of the obtained images correct enough for the subsequent step of image recognition.
In order to allow this flexibility relating to the distance between a fixed focus camera and the object of interest, an available technical solution is to improve the depth of field of the camera. The improved depth of field of the camera should be adequate for the specific use and purpose of the optical device.
The US Patent Application US2007/0119942 discloses a method for improving the depth of field of a camera used in a linear optical barcode reader. The linear optical barcode reader according to US2007/0119942 comprises a camera with a photosensitive element or sensor and an optical receiving device, with one or more lenses, for forming an image on the sensor. The optical receiving device has an optical receiving path or optical axis. The device comprises in the optical axis of the optical receiving device, upstream or downstream of the objective, a diaphragm to improve the depth of field of the camera. This diaphragm has the form of an opaque screen stopping the light, with a light passing aperture. In use, the rays which pass through the aperture contribute to the formation of the image onto the sensor. By contrast, the light beams that are intercepted will not contribute to the formation of the image.
According to US2007/0119942, the effect of the presence of the diaphragm in the optical axis of the camera is that the depth of field of the camera is increased when compared with a camera which does not comprise the diaphragm.
The solution according to US2007/0119942 provides an improvement of the depth of field in one specific direction. This is due to the rectangular shape of the light passing aperture. The effect is that the solution according to the prior art can be used for a specific task such as reading a linear optical barcode. However, the solution according to the prior art document is not adapted to provide a general solution for increasing the depth of field of cameras used in an optical device for analysing objects with arbitrary shapes, such as 2-D optical codes. The solution according to US2007/0119942 would not be adapted to improve the depth of field of a camera used for a general task, such as a sample level detection.
Japanese patent application JP2003-098426 discloses a camera using a specific diaphragm to improve the depth of field of the camera. The specific diaphragm consists of a central part for transmitting only infrared rays and an outside part for transmitting only visible light. According to JP2003-098426, the use of the specific diaphragm in combination with specific lighting conditions eliminates the needs for a diaphragm with an auto iris control system. However, this solution is expensive and complex to operate.
The object of the invention is to provide an improved optical device with a camera and means for improving the depth of field of said camera and means for improving the quality of an image to be taken of an object located in the improved depth of field, wherein the improvement of the depth of field is not limited to a specific directional use of the optical device.